Note: Descriptions are shown in the official language in which they were submitted.
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il nisclosure of Invention
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" This invention relates to cooling apparatus and, more
¦I specifically, to such apparatus which is energy efficient, and
which accommodates large variations in evaporator heat loading.
~¦ It is an ob~ect of the present invention to provide improved
5 ¦1 air conditioning apparatus.
¦ More specifically, it is an object of the present invention
to provide improved air conditioning apparatus which is energy
efficient employing water coil cooling ra-ther than direct expan- ¦
I sion cooling when possible and which reduces compressor energy
¦ requirements, and which accommodates the resulting large
¦ dynamic range in direct expansion evaporator thermal loading.
i,¦ It is another object of the presen-t invention to provide
,1 improved direct expansion equipment including a water cooled
condenser which does not require water flow modulation to
maintain system coolant pressure under light loading conditions. I
I The above and other objects of the present invention are
li realized in specific illustrative air conditioning apparatus
¦¦ which includes at least one cascaded array of a water cooling
¦¦ coil and an evaporator between air return and supply ports. The
20 ¦! evaporator is included in a closed dlrect expansion cooling
I~ subsystem having a compressor, and a water cooled condenser
,' continuousIy receiving all of the circulated water coolant.
i~ `Air cooling is first effected by the water cooling coil
i~ (assuming sufficiently low circulating water temperature), and
2~ ~ the remaining heat load accommodated by the evaporator. Pressure
regula-ting apparatus and the like is employèd to vary the
active surface area of the condenser and maintain evaporator
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pressure to accommodate the wide dynamic range of thermal loading impress-
ed on the direct expansion subsystem.
Thus, in accordance with a broad aspect of the invention, there
is provided, in combination in cooling apparatus, a cascaded combination
of a water cooling coil and a contiguous coolant evaporator, direct
expansion refrigerant means including the cascaded connection of a com-
pressor, a water cooled condenser and said evaporator, water circulating
means including a first valve and a first bypass connecting to said water
cooling coil for selectively supplying water to or around said cooling
coil, and means for passing the water flowing through or bypassed around
said water cooling coil through said water cooled condenser.
The above and other features and advantages of the present
invention will become more clear from the following detailed description
of a specific, illustrative embodiment thereof presented hereinbelow in
conjunction with the accompanying drawing.
Referring now to the drawing, there is shown air conditioning
(cooling, but see below) apparatus embodying the principles of the present
invention. In overview, return air flow typically passing through return
air ducts ~not shown) passes through cascaded cooling elements comprising
a heat exchanging water cooling coil 10 and a heat exchanging evaporator
42. From the output side of the evaporator 42, the now cooled air fIows,
either directly or via further conduits under fan action to the ambient
environment receiving the conditioned air. One cascaded cooling coil
10 - evaporator 42 combination, together with their ancillary equipment,
is shown in the drawing and a second such combination generally indicated.
It l~ill be appreciated that any number of such cooperating structures
may be employed, depending upon ~he cooling capacity desired.
By way of overview and general desideratum, cooling is accom-
plished by the cooling coil 10 whenever ~he system water cooling fluid
is of a sufficiently low temperature (e.g., below 70 F) to in fact
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accomplish such cooling purposes. To the extent that the circulating cooling
water is suff;cient to effect cooling, it relieves (sometimes partially;
sometimes totally) the thermal cooling load impressed on the system evapora-
tor(s) 42, each of l~hich requires, inter alia, a relatively high
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¦1 energy consumptive compressor 40. Thus where adequate and
II relatively cold cooling water available (as is often the case
¦i for the internal cooling of a large building in winter), the
I cooling water effects a substantial portion of -the cooling load.
I, Correspondingly, under summer conditions where the gross cooling
re~uirement is larger and the circulating water supply at a
higher temperature, rela-tively more cooling is required by the
¦ evaporator 42 with its ancillary apparatus. When more than one
I cooling coil 10 is utilized, they are successively turned on and
¦ all employed before any direct expansion cooling effected. The
foregoing system is energy efficient since maximum use is made
of the thermal absorptive capacity of the circulating water
cooling fluid requires relatively little energy input vis-a-vis
direct expansion cooling. Moreover, when the direct expansion
Ij apparatus is on but relatively lightly loaded, substantial
IIl compressor driving electrical energy is saved as well. However,
this impresses a large dynamic range for the cooling capacity
required of the evaporator 42 and its driving equipment
~ ("the direct expansion apparatus"). All of this is accomplished
I by the Fig. 1 apparatus which will now be considered in detail.
A cooling water supply is maintained via a per se
I conventional cooling tower and pump 16 which supplies cooling
¦ water via a supply line 18 to valves 12 and 1~ (two valves being
II employed for the assumed two sections of water cooling coil lo?.
1l Wate~ entering valve 14 from the supply line 18 reaches a conduit ¦
Il 31 either directly via bypass conduit portions 27 and 28 (when
~I no cooling is effected by the water cooling coil 10 shown); or
!~ via conduit 25, the cooling coil 10 and pipe 29 when cooling is
~ in fact being implemented by the coil 10~ A similar wa-ter flow
I through or around a second water cooling coil (not shown) is
effected by the valve 12 in the manner indicated. Valves 12 and
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i~ i re operated by control signals V1 and V2, respec-ti~ely,
'supplied by a relay and loyic circuit 3~ discussed below. Thus,
I depending upon the state of control signals Vl and V2, none, the
¦iwater coll 10 shown, or bo-th water cooling coils are in an
!,active (cooling) state.
The cooling water in conduit 31 (whekher or not previously
j~passing through one or both of the water cooling coils 10)
¦ continuously flows through a water cooled condenser ~5 included
lin the direc-t expansion cooling system loop, or subsys-tem,
~finally returning to the cooling tower and pump 16 via conduit
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j The composite cooling apparatus shown in the drawing may
jlbe employed in systems adapted for year round use. Thus, such
!icooling apparatus is utilized even in colder environments during
'Icolder periods - as for cooling in a computer room context to
iimaintain relatively sensitive electronic equipment under proper
¦temperature and humidity conditions; to cool the interior of a
jlarge office building structure subject to large illumination
¦heat loads; and the like. To the extent that the ~7ater coolant
icirculating in the above described water circulation paths is
maintained in a useful cooling range ~y the cooling tower 16
(e.g., at a temperature below 70~ F.j it is used for cooling
employing the water cooling coil(s) 10 employed in -the system
~' (the coils 10 being used on a monitonically increasing basis as
llambient temperature increases). Thus, the composite system
, makes use of the cooling capacity of the circulating water (again,
much less expensive than the energy required to drive compressors
and the like for direct expansion cooling) to the maximum extent
, that useful cooling may be effected thereby. ~loreover, when
~ on but lightly loaded, ener~y is saved in clriving the compressor
as well.
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The Fi~ure 1 arrangement employs two independent direct '
,¦ expansion cooling subsystems for the assumed two evaporators 42
jl (only one being shown in detail, and the other being iden-tical
Il thereto) such -that the evaporators ~2 included in such sub-
,' systems accommodate whatever thermal work load remains af-ter
ll-the cooling capacity of -the water cooling coils 10 proves per se
¦l insufficient. Accordingly, the thermal heat exchanging loads
impressed on the direct expansion subsystems varies very
markedly (herein over a'"large dynamic range").
This large dynamic range would create severe operational
dif~iculties for prior art direct expansion cooling structure.
Principally, the active heat exchanging sur~ace areas for the
!l evaporator and water cooled condenser in such system (scaled for
¦l peak thermal loads) is much too large for ~ery light thermal
1! loading periods. The result in such prior art systems would be
!' a greatly reduced evaporator pressure with -the possibility of
substantial direct expansion liquid coolant (e.g., Freon) passing
from the evaporator into a compressor and subsequently damaging
the compressor.- Moreover, under light loading conditions, the
evaporator in such apparatus over-cools the air, thereby removing
needed moisture from the air and also reauiring a subsequent
¦j humidification and re-heat operations. To prevent excessive
condenser cooling pressure reduction under low loading conditions,
j~ valves have here,to~ore been included in the series water flow
¦,~ cooling path to the condenser to modulate water flow (and
il terminate condenser over-coolin~). However, this has required
relatively expensive valves to interrupt wa-ter flow in high
water pressure situations, as where the water cooled condenser
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1' is moun-ted low in a high building structure.
!i The above and o-ther difficult:ies are overcome in the
¦I direct expansion subsystem shown in the drawing which readily
¦~ accommodates the large thermal dynamic range impressed on the
5 11 evaporator(s) 42. Each direct expansion subsystem basically
comprises the c~scade connectian o~ a compressor ~ t~r ~ol@d
condenser ~5, head pressure regulating valve 47t receiver tank
48, solenoid valve 50, expansion valve 51, the evaporator 42,
I¦ an evaporator pressure regulating valve 56, and a suction line
¦ accumulator 54. A differential check valve 52 connects the
I gas phase coolant (Freon) output port of compressor 40 with the
¦ receiver 48. The basic elements A0, 45 and 42 perform the con-
ventional functions associated therewith for direct expansion
I cooling. The compressor 40 receives the incoming gas from the
¦ output ol evaporator 42 and compresses it, also supplying the
¦ coolant in a gaseous sta-te to the condenser 45. The condensed
. gas in condenser 45 is cooled by heat exchange with the water
j flo~ therearound, exiting from the condenser 45 as a liquid.
The coolant liquid output of condenser 45 is supplied as an
I input to evaporator 42 in which it changes to gaseous state,
absorbing heat from the return air flow passing through the
i evaporator 42. The gaseous coolant completes the direct expan-
sion cycle by return to the compressor 40.
As a first matter, the Figure 1 equipment operates to reduce
¦I the cooling effected on the coolant (Freon) gas entering the
! condenser 45 under relatively-light loading conditions, thereby
maintaining the~pressure in the li~uid Freon entering the
evaporator 42 under such light loading conditions. This is
basically accomplished by the head pressure valve 47 serially
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jincluded between the condenser 45 and -the receiver tank 48 to
main-tain a preset minimum pressure in the condenser. A typical
¦valve 47 simply includes a variable orifice (or an open/closed
Imod~llated orifice) which restricts the flow of liguid content
Ipassing therethrough -to maintain a minimum back pressure
required to overcome a res-trictive bias before fluid exits the
valve. Such valves 47 are a matter of common experience to those
skilled in the art, and may illustratively comprise a spring
biased bellows or seal such that the pressure entering the valve
must overcome the spring pressure before liquid coolant can pass
through the valve.
¦ The result of the pressure induced by the valve 47 in and
through the condenser 45 is to cause a liquid build up in the
¦ latter portion of the tubes in the condenser 45 - thereby
l¦ effectively reducing the heat exchange effected by the water
¦I circulating through the condenser from conduit 31 and the Freon
coolant being -onverted from gas to liquid state in the condenser.
I Such a back-up of fluid state coolant, starting from the exit
¦ end of the condenser 45 reduces the effective thermal interchange
¦ between the water and Freon, since the water has relatively
I little effect on that portion of the condenser 45 tubes having
¦ liquid state Freon coolant therein. This occurs since the water-
¦ liquid Freon heat exchange is by conduction only; while that
portion of the condenser 45 tubing having gaseous state Freon
' is càpable of removing the heat of condensation of the Freon
and passing it to the circulating water. Thus, under light
loading conditions for the direct expansion eauipment, a
, relatively large amount of the liquid state Fre~n reposes in the
i~ condenser 45 and a relatively small amount thereof is disposed
i in the bottom oE the receiver tank 48. Correspondingly, during
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i¦ periods oE heavy loading, -there is relatlvely little Freon
liquid in the condenser ~5, with the principal portion of the
,I remaining Freon liquid not othen7ise required by the system
¦, being disposed in the bottom of the receiver tank ~8.
~I To maintain the pressure in the cooling subsystem between
the output of head pressure control valve 47 and the evaporator
1 42, the dif~erential check valve 52 passes gaseous coolant into
¦ the receiver tan~ ~8. The pressure in receiver tank ~8 through
¦ solenoid valve 50 and into expansion valve 51 is thereby
¦ basically maintained at -the output value ~or the compressor 40
¦ less the operative préssure drop for the chec~ valve 52 (e.g.,
25 psig). Thus, the water cooled condenser 45 is maintained
operative under widely varying thermal loading by modulating the
I Freon liquid state material reposing therein while the input
li pressure to the'evaporator ~2 is maintained sufficient by the
¦I shunt path from the compressor 40 through the check valve 52.
The variable thermal loading on evaporator 42 is principally
accommodated by evaporator pressure regulating valve 56 which
¦ maintains a fixed pressure in evaporator 42. This maintains the
¦ evaporator coolant temperature at an acceptable minimum value,
preventing the evaporator temperature from monitonically
decreasing as load lightens which would otherwise be the case.
Accordingly, overcooling (and the conco~itant excess dehumidi-
¦' fication) is avoided.
!~ The resulting low input,pressure to the compressor ~0caused by valve 56 during relatively light loading thermal
conditions results in a lessened driving electrical energy
re~uirement for the compressor. This further enhances the
, energy saving attribu-tes of the composite Fig. 1 system. Further
in this regard, a pressure switch ~1 (e.g., a pressure relay
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wi-th a time delay/minimum oEE perioa) may be employed to pro-tect
the compressor ~0 by shutting down the compressor when the
incoming gas flow (pressure) .falls below a predetermined minimum
I value.
5 ¦ The expansion valve 51, capable of modulating to 10% of
full capacity, effects its per se well-known ~unction to reduce
the liquid pressure input to the evaporator 42 from the output
vaiue of receiver 48. The valve 51 senses the temperature of
the gaseous Freon at the output of evaporator 42 and regulates
¦ its degree of liquid flow constriction (pressure) to assure that
the coolant at the output of the evaporator 42 is in a
superheated (and thus definitively gaseous) state (again~
to avoid injury which results should liquid enter the compressor
Il 40)-
¦ A suction line accumulator 5~ is employed on the input side
If the compressor. The accumulator 54 may comprise a sump, tank
¦ or the like to trap any liquid Freon inadvertently passing through
the evaporator 42 to protect the compressor 40~ Finally, the
solenoid valve 5b is opened and closed with the same control
signal (e.g., Cl) as the compressor ~0 to prevent liquid from the
receiver 48 flowing into the evaporator 42 when the compressor
is off, to again ultimately protect the compressor.
Thus, the above functional description of the Figure 1
direct expansion subsystem shown, illustrative of all other sub-
¦, systems, readily absorbs the large dynamic range of thermal loads
¦¦ impressed thereon by simply modulating the active surface of
¦ condenser 45, and regulating evaporator pressure in the manner
¦. above described.
I' As above described, the control sequence for the composite
cooling apparatus of the drawing is to first use one stage of
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I wa-ter coolin~ coil; then bo-th stages; followed by first one and
then both oE the direct expansion evaporators 42 as the thermal
¦'load on the system increases. Should the water be above its
jluseful cooling ranye, then either one or both of the evaporators
1~42 are utilized without the water coil pre-cooling. Assuming
the Boolean variables Vl, V2, Cl, and C2 are control signals for
, the water cooling valves 12 an~ 14 and the compxessors (compressor
j40 and associated solenoid valve 50) in the two direct expansion
¦subsystems, respectively, Boolean expressions for the control
llogic is as follows:
, Vl = WT Tl ( 1 )
V2 = WT T2 (2)
Cl = I~T Tl ~ T3 ( 3 )
I C2 = ~T T2 -~ T4 (4)
jlwherein WT identifies the output of a water sensing thermostat
¦i 31 signalling that the fluid in water supply 18 is in a useful
!I range (e.g., below 70F.); and Tl - T4 are temperature signalling
¦ conduct closures from a controlled environment (e.~., a room) air
¦ temperature sensing thermostat 32 with -the temperatures increas-
ing from Tl to T4. Thus, a review of equations (1)-(4) will
show that the valves 12 and 14 operate when the thermostat 31
j senses useful water and the room thermostat 32 provide the outputs
¦T1 and T2, respectively. The compressor 40 and solenoid valve 50
¦ are turned on to actuate the first evaporator subsystem when the
1l cooling water is too warm for pre-coollng and the room thermostat
¦~ signals that the turn on threshold temperature Tl is reached
¦~ (WT Tl) or when the -tempera-ture T3 is reached. Similarly, the
second compressor is turned on either when the higher temperature
'~ T4 is reached or when -the tempera-ture T2 is reached if no ~ater
pre-cooling is being effec-ted (WT T2). A particular form of
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control relay logic is shown in the drawing, the con-tacts being
shown in conventional detached form assuming relays (not shown)
~WT to report water -temperature from water thermos-tat 31 and
!llassuming outputs Tl-T~ from the room thermostat.
¦¦ Thus, the above described arrangement has been shown to
efficiently and automatically effec-t cooling to a controlled air
~¦ stream, first using the full capacity of a circulating water
¦¦ coolant. The arrangement operates without any requirement or
¦ valve control of compressor water coolan-t and functions notwith-
I standing a wide divergence in the thermal load applied -to the
¦ direct expansion subsystems. While the arrangement shown in the
¦ drawing has controlled only the temperature of the conditioned
¦ air supply, any desired reheat and humidifying apparatus well-
I known to those skilled in the art may be utilized to further
~ control humidity and temperature for a regulated air environment.
l The above described arrangement is merely illustrative of
¦ the principles of the present invention. Numerous modifications
¦ and adaptations thereof will be readily apparent to those skilled
I in the art without departing from the spirit and scope o~ the
present invention. Thus, for example, the relay control logic
shown may be replaced by any well-known digital logic family and,
indeed, a microprocessor may be utilized to receive and process
the digitized outputs of water and room temperature sensing
analog or digital thermostats.
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